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 #include &lt;QtGui&gt;

 #include &quot;imagecomposer.h&quot;

 static const QSize resultSize(200, 200);

 ImageComposer::ImageComposer()
 {
     sourceButton = new QToolButton;
     sourceButton-&gt;setIconSize(resultSize);

     operatorComboBox = new QComboBox;
     addOp(QPainter::CompositionMode_SourceOver, tr(&quot;SourceOver&quot;));
     addOp(QPainter::CompositionMode_DestinationOver, tr(&quot;DestinationOver&quot;));
     addOp(QPainter::CompositionMode_Clear, tr(&quot;Clear&quot;));
     addOp(QPainter::CompositionMode_Source, tr(&quot;Source&quot;));
     addOp(QPainter::CompositionMode_Destination, tr(&quot;Destination&quot;));
     addOp(QPainter::CompositionMode_SourceIn, tr(&quot;SourceIn&quot;));
     addOp(QPainter::CompositionMode_DestinationIn, tr(&quot;DestinationIn&quot;));
     addOp(QPainter::CompositionMode_SourceOut, tr(&quot;SourceOut&quot;));
     addOp(QPainter::CompositionMode_DestinationOut, tr(&quot;DestinationOut&quot;));
     addOp(QPainter::CompositionMode_SourceAtop, tr(&quot;SourceAtop&quot;));
     addOp(QPainter::CompositionMode_DestinationAtop, tr(&quot;DestinationAtop&quot;));
     addOp(QPainter::CompositionMode_Xor, tr(&quot;Xor&quot;));

     destinationButton = new QToolButton;
     destinationButton-&gt;setIconSize(resultSize);

     equalLabel = new QLabel(tr(&quot;=&quot;));

     resultLabel = new QLabel;
     resultLabel-&gt;setMinimumWidth(resultSize.width());

     connect(sourceButton, SIGNAL(clicked()), this, SLOT(chooseSource()));
     connect(operatorComboBox, SIGNAL(activated(int)),
             this, SLOT(recalculateResult()));
     connect(destinationButton, SIGNAL(clicked()),
             this, SLOT(chooseDestination()));

     QGridLayout *mainLayout = new QGridLayout;
     mainLayout-&gt;addWidget(sourceButton, 0, 0, 3, 1);
     mainLayout-&gt;addWidget(operatorComboBox, 1, 1);
     mainLayout-&gt;addWidget(destinationButton, 0, 2, 3, 1);
     mainLayout-&gt;addWidget(equalLabel, 1, 3);
     mainLayout-&gt;addWidget(resultLabel, 0, 4, 3, 1);
     mainLayout-&gt;setSizeConstraint(QLayout::SetFixedSize);
     setLayout(mainLayout);

     resultImage = QImage(resultSize, QImage::Format_ARGB32_Premultiplied);

     loadImage(&quot;:/images/butterfly.png&quot;, &amp;sourceImage, sourceButton);
     loadImage(&quot;:/images/checker.png&quot;, &amp;destinationImage, destinationButton);

     setWindowTitle(tr(&quot;Image Composition&quot;));
 }

 void ImageComposer::chooseSource()
 {
     chooseImage(tr(&quot;Choose Source Image&quot;), &amp;sourceImage, sourceButton);
 }

 void ImageComposer::chooseDestination()
 {
     chooseImage(tr(&quot;Choose Destination Image&quot;), &amp;destinationImage,
                 destinationButton);
 }

 void ImageComposer::recalculateResult()
 {
     QPainter::CompositionMode mode = currentMode();

     QPainter painter(&amp;resultImage);
     painter.setCompositionMode(QPainter::CompositionMode_Source);
     painter.fillRect(resultImage.rect(), Qt::transparent);
     painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
     painter.drawImage(0, 0, destinationImage);
     painter.setCompositionMode(mode);
     painter.drawImage(0, 0, sourceImage);
     painter.setCompositionMode(QPainter::CompositionMode_DestinationOver);
     painter.fillRect(resultImage.rect(), Qt::white);
     painter.end();

     resultLabel-&gt;setPixmap(QPixmap::fromImage(resultImage));
 }

 void ImageComposer::addOp(QPainter::CompositionMode mode, const QString &amp;name)
 {
     operatorComboBox-&gt;addItem(name, mode);
 }

 void ImageComposer::chooseImage(const QString &amp;title, QImage *image,
                                 QToolButton *button)
 {
     QString fileName = QFileDialog::getOpenFileName(this, title);
     if (!fileName.isEmpty())
         loadImage(fileName, image, button);
 }

 void ImageComposer::loadImage(const QString &amp;fileName, QImage *image,
                               QToolButton *button)
 {
     image-&gt;load(fileName);

     QImage fixedImage(resultSize, QImage::Format_ARGB32_Premultiplied);
     QPainter painter(&amp;fixedImage);
     painter.setCompositionMode(QPainter::CompositionMode_Source);
     painter.fillRect(fixedImage.rect(), Qt::transparent);
     painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
     painter.drawImage(imagePos(*image), *image);
     painter.end();
     button-&gt;setIcon(QPixmap::fromImage(fixedImage));

     *image = fixedImage;

     recalculateResult();
 }

 QPainter::CompositionMode ImageComposer::currentMode() const
 {
     return (QPainter::CompositionMode)
            operatorComboBox-&gt;itemData(operatorComboBox-&gt;currentIndex()).toInt();
 }

 QPoint ImageComposer::imagePos(const QImage &amp;image) const
 {
     return QPoint((resultSize.width() - image.width()) / 2,
                   (resultSize.height() - image.height()) / 2);
 }</pre>
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